Now TMZ have reportedly uncovered more details about Selena's surgery, with a number of sources saying that the 25-year-old had to be rushed to hospital while in Chicago for boyfriend The Weeknd's tour.

According to the insiders, Sel had been visiting The Weeknd - real name Abel Tesfaye - when she went into kidney failure, with Abel accompanying her to the hospital.

It's believed that Selena was already on a kidney transplant list at that point.

Selena first revealed that she had been diagnosed with autoimmune disease lupus in 2015, slamming tabloid media for misjudging her admittance to an Arizona rehab facility the year before.

“I was diagnosed with lupus, and I’ve been through chemotherapy," she said at the time. "That’s what my break was really about.

"I could’ve had a stroke. I wanted so badly to say, ‘You guys have no idea. I’m in chemotherapy. You’re assholes.'"

Lupus is a chronic disease which causes inflammation in certain organs and can affect the skin, heart, lungs, brain, joints and kidneys; NBC News reports that as many as 60 per cent of lupus sufferers will develop kidney disease at some point.

While Selena hasn't revealed exactly what form of lupus she has been diagnosed with, there is one particular type - lupus nephritis - that attacks the kidneys and surrounding blood vessels "like a disease".